Laser diode arrays are in general used in a wide variety of industrial and research applications. Pluralities of diode bars are mounted on a substrate to provide the multiplied power of numerous bars, versus the effect offered by a single bar. For arrays that are operated in harsh environments such as high temperatures or rapidly changing temperatures it is desired that the entire array assembly be assembled with high temperature, so-called hard solders. In arrays that are fabricated with high temperature solders it is imperative to minimize the stress induced in the laser bar from the assembly process. To optimize the efficiency of a multiple diode bar array the materials used must also have high electrical conductivity and thermal conductivity. Historically, this has required the use of materials that have different thermal expansion properties. In a hard soldered assembly small thermal expansion mismatches can cause stress on the bars and hence reliability issues. In addition good alignment of the bars is necessary to maintain high efficiency, good performance, and high reliability.
Laser diode arrays characteristically have large heat dissipation per unit area of the laser diodes. This increase in temperature results in a limitation on output intensity. As the temperature increases and decreases, the device is subject to thermal cycling, shortening the life of the array. Furthermore, at higher temperatures the laser emission will be shifted in wavelength due to temperature induced shifts of the semiconductor bandgap.
Several patents have been directed to improve the heat removal capability of laser diode arrays. Specifically, array designs have incorporated microchannel cooling as a means for heat removal. Microchannel coolers are small devices with channels etched therein to supply a coolant in close proximity to the heat source. See for example, U.S. Pat. Nos. 5,105,429; 5,311,530; 6,480,514; 6,865,200 and 7,016,383.
These prior art patents require complex assemblies involving many individual components joined together mechanically and using O-rings to seal the fluid paths. This makes assemblies of micro-channel coolers somewhat fragile, prone to fluid leaks and misalignment. In addition, the small fluid channels used in micro-channel coolers are prone to blockage and thus require filtered water as the cooling fluid which adds to operating costs. The high water velocity in the channels also leads to erosion of the channels, leading to failure of the assembly. Moreover, since the water is in the electrical path it must be electrically insulating or de-ionized. De-ionized water is somewhat corrosive, and thus requires corrosive resistant materials and coatings to prevent the device from rapidly degrading.
Several prior art designs also have incorporated macrochannel cooling as a means for heat removal. However, macrochannel cooler assemblies have suffered from an inability to meet the cooling performance of micro-channel assemblies and have therefore been limited to certain low power applications or applications where the laser diode bars can be placed far enough apart to enable the heat generated in each bar to be removed. In addition macrochannel cooler assemblies have typically employed soft low temperature, so-called soft solders to permit movement between thermally expansion mismatched materials. While soft solders permit movement and thus reduce stress, they are subject to fatigue type failures and can creep over time leading to catastrophic failure.